The present invention generally relates to semiconductor chip packaging. More particularly, the present invention relates to a center bond flip-chip semiconductor device and a method for making it.
Semiconductor device packaging techniques are well known. In some conventional packaged devices a die is attached to a carrier, and contacts of each are electrically connected. In one such packaged device, called a flip-chip device, a semiconductor chip is flipped and bonded with a carrier such that contacts of the chip face and bond to contacts of the carrier.
With reference to FIGS. 1-3, a conventional center bond flip-chip device 10 is shown including a die 30 and a carrier 11 fabricated from a flexible substrate 12, a conductor layer 14 which includes a polyimide core 13 and a plurality of conductive traces 15, and an elastomeric layer 16. The flexible substrate 12 is formed of a material exhibiting high temperature stability as well as high mechanical rigidity. The substrate 12 may be a flexible tape, such as, for example, a polyimide tape. Two commercially available polyimide tapes, KAPTON(copyright) from E. I. DuPont Nemours and Company and UPILEX(copyright) from Ube Industries, Ltd., can be used to form the substrate 12.
The elastomeric layer 16 includes a first portion 17 and a second portion 19 of generally equal size and separated by a gap 22. The elastomeric layer 16 may be formed of a silicone or a silicone-modified epoxy.
The conductive traces 15 may be located within or on the polyimide core 13 in a variety of ways. One way, which is an addition method, is to build up the conductive traces 15 on the polyimide core 13 through electrolytic deposition. The electrolytic deposition may be accomplished with a mask, or if performed without a mask, a subsequent etching step may be employed to create the conductive traces 15. Other suitable methods include sputter coating and laminating a sheet of conductive material, such as copper, and etching away excess copper to form the traces 15.
The conductive traces 15 are each electrically connected to a solder ball 28 within an inset 26. Although a single solder ball 28 is shown in FIGS. 1-2, it is to be understood that the number of solder balls 28 should correspond with the number of conductive traces 15 within the conductor layer 14. The solder balls 28 are used to mount the flip-chip device 10 to a circuit board or other electrical structure (not shown).
A solder mask 18 is positioned on the conductor layer 14 within the gap 22. As illustrated, the gap 22 is rectangularly shaped, although any configured gap will suffice as long as the solder mask 18 is not covered by the elastomeric material 16.
The die 30 is shown in dotted line above the carrier 11. In use, the die 30 is positioned on the elastomeric material 16 of the flip-chip carrier 11. The flip-chip carrier 11 is electrically connected with the die 30 by way of suitable conductive connecting structures, such as, for example, solder balls 24 positioned within a gap 20 of the solder mask 18. The solder balls 24 are in electrical connection with respective conductive traces 15 through a gap 20 in the solder mask 18 and with suitable contacts on the die 30.
Conventional center bond flip-chip semiconductor devices of the type shown in FIGS. 1-3 have several disadvantages. One is that the solder mask 18 on the carrier 11 has the large, unsupported central gap 20 in which a plurality of solder balls 24 are positioned. The lack of support in the large singular gap 20 allows movement of the solder balls 24 causing them to sometimes contact with one another. Further, the solder mask 18 is positioned at a distance (currently around 150 micrometers) from the elastomeric material 16 due to poor adhesion between the solder mask 18 and the elastomeric material 16. As a consequence, a minimum possible size of the flip-chip device 10 is at least partly determined by the distance between the solder mask 18 and the elastomeric material 16.
There is, therefore, a need for a center bond flip-chip semiconductor device design which alleviates to some extent these disadvantages.
The present invention provides a center bond flip-chip semiconductor carrier including a flexible substrate, a core material with a plurality of conductive traces positioned on the flexible substrate, and a die attach material formed on the layer of conductive material. The die attach material includes a plurality of pockets, each for confining an interconnect conductor, such as a solder ball, over a conductive trace.
The present invention further provides an electronic system including a processor-based system, a semiconductor die in electrical connection with the processor-based system, and a die carrier connected to the semiconductor die. The die carrier has a flexible substrate, a core material with a plurality of conductive traces positioned on the flexible substrate, and a die attach material formed on the layer of conductive material. The die attach material includes a plurality of pockets, each for confining an interconnect conductor, such as a solder ball, over a conductive trace.
The present invention further provides a method for making a carrier for a semiconductor device. The method includes the steps of forming a layer of elastomeric material over a layer of conductive material in the form of traces and forming at least one pocket in the layer of elastomeric material extending to a trace of the conductive material.
The present invention further provides a method for making a carrier for a semiconductor device. The method includes locating at least one conductive trace on a core material, forming a die attach material over the core material, and forming a plurality of pockets in the die attach material extending to the at least one conductive trace.
The foregoing and other advantages and features of the invention will be more readily understood from the following detailed description of the invention, which is provided in connection with the accompanying drawings.